1. Field of the Invention
This invention relates to an improved process for the preparation of esters of carboxylic acids and in particular to the preparation of lower alkyl (1 to 4 carbons) esters of carboxylic acids (8 to 22 carbons) which are useful in the preparation of beta diketones which are water insoluble and water immiscible and suitable for extraction of metal values.
2. Statement of Related Art
Esters of acids are important from the industrial standpoint as a great variety of commercial products are based on such esters. The classical method of preparing esters involves the reaction of an acid with an alcohol, usually in the presence of a catalyst to afford an ester and water. EQU RCOOH+R'OH.fwdarw.RCOOR'+H.sub.2 O
The process is reversible and quantitative yields by simple reaction of the acid and alcohol are not obtained in the equilibrium reaction mixture. The catalyst's sole function is to hasten the attainment of equilibrium and does not affect the final composition at equilibrium. Generally, equilibrium is forced to the right in the equation by the removal of water as it is formed such as by application of mild vacuum to the reaction mixture. Alternative methods include the addition of other materials to form an azeotropic mixture with the water which azeotropic mixture is removed. Another attempt to effect high conversion requires the addition of large molar excesses of either the acid or alcohol, usually the least expensive material, or material with the lowest boiling point being used in excess in commercial practice.
Lower alkyl (1 to 4 carbon) esters of carboxylic acids have been employed in the past to prepare .beta.-diketones which are useful in the extraction of metal values as described in commonly assigned U.S. Pat. No. 4,175,012. As described therein, the diketone is prepared by condensation of the ester with a compound containing an acetyl moiety in the presence of sodium hydride and an inert organic solvent. In the preparation of the ketone it is desirable that the ester be of a high purity.